spacer Making PCB Boards

There are various methods for the hobbyist to make PCB boards. I use the toner transfer method because it is cheap and requires relatively little setup or equipment. You need access to a laser printer or photocopier, an iron, and you'll need an etching solution.

Printing the Pattern

The method works by printing the desired pattern onto a piece of paper using a laser printer or a photocopier. The printer MUST use toner. Inkjet printers won't work. You'll want a nice dark image without splatter or speckling. Any imperfections will be transferred to the copper-clad board.

Laser Printed PCB Pattern

The type of paper you use is critical. Paper with too much fibre or texture will adhere to the toner too strongly, or will cause the toner to 'bleed' sideways.

I've had decent success with the cheap STAPLES brand Glossy Photo Paper. I bought a 100 pack of 4" x 6" sheets. Other glossy inkjet photo papers will probably work just as well. There are also commercial transfer products like Press-n-Peel Blue although I've not used them.

I recently purchased an interesting product called Dissolvo. This is a paper-like product that dissolves in contact with water. It was originally developed for making gas dams for exotic gas welding. More recently it's become available in decent size sheets via magic shops. I purchased mine from the Magic Warehouse as 8-1/2x 11 sheets at 35¢ each. You can print on it with a laser printer without problem. It is a bit thin, so I tend to tape pieces onto a regular sheet of paper using Scotch tape along the leading edge. I just cover the pattern I'm printing so as not to waste too much of it.

Transferring the Pattern

The first step to transferring the pattern is to prepare the copper-clad board. You'll need to scour the copper side (and the opposite side if you want to transfer the component layout image). Some people use plastic scouring pads. I use a 1500 grit, wet sanding paper. One sheet lasts a long time.

The idea is to clean off any oxidation from the copper side, and to roughen the board on the opposite side. No need to press hard but be thorough. Rinse and dry the board with a oil-free tissue or towel.

The printed pattern is placed toner side against a piece of copper-clad board. An iron is used to heat the paper, melting the toner in the pattern and pressing it onto the copper-clad board.

You'll need to experiment with how hard to push and how hot to make the iron. I bought the cheapest iron (KitchenWorks) I could find at Canadian Tire. For the STAPLES glossy paper I set the temperature to Cotton (hottest). If the iron is too hot, the toner gets too fluid and can smear. Too cold and the toner does not adhere well enough. When I used dissolvo, I had to dial down the temperature a bit since the paper started to turn brown (i.e. burn).

Regarding ironing, I tend to tack the pattern into place by heating one half of the board first. I don't press really hard for fear of causing the pattern to shift. Edges tend to need extra attention. This is where I tend to find poor adhesion if it occurs.

Removing the Paper

Once the board is cool, it is immersed in water. The STAPLES glossy inkjet paper tends to come off in several layers. First the backing paper comes off. Secondly inner layers come off. Then finally, the glossy layer. You can firmly rub your thumb back and forth to remove trace bits of paper. The toner should not come off. If it does, your iron may be cool, you may not be pressing hard enough during ironing, or the board might not have been clean.

The Dissolvo, falls apart into many short fibres. There are still residual fibres adhering to the toner so some brushing with a soft toothbrush is still required. I've only made a few boards using Dissolvo but so far it looks more difficult to use than the glossy paper.

If the pattern is not good, you can remove the toner with acetone or nail polish remover and try again. Below you can see a few spots where a few paper fibres still adhere giving the toner a white colour. Also in area 2 you can see a small break in the toner caused by a defect in my laser printer's photo drum. This is not significant, however, and will easily be bridged by solder during construction.

Iron Transferred PCB pattern

Etching the Board

Next, the copper-clad board is etched to remove the unprotected copper, leaving behind the pattern we printed. The toner that is left behind on the copper-clad board is an effective etch resist. There are three common etching solutions that I am aware of.

Etched PCB

Ferric Chloride

Warning: Ferric Chloride is corrosive and stains! If you get it on your skin, rinse the area immediately. Similarly it will stain and/or corrode most non-plastic surfaces that it contacts so be neat, tidy and clean up any spills immediately. I have occasionally gotten small amounts of this solution on my fingers and suffered no ill effects but your mileage may vary.

Ferric Chloride is what I tend to use. I buy the ready mix although you can also purchase it in powder form. I use the polyethylene (flexible plastic) lid of a CD spindle as my etching tank. I pour in enough Ferric Chloride to make a layer about 1/2" deep. I then microwave this for about 40 seconds to heat it up. Used properly, the ferric chloride solution gives off virtually no fumes and I use it indoors with no special ventilation.

Warning: If you heat it too much it will start to give off brown smoke which is NOT healthy to breath so STOP. You can still use the solution. Just let it cool for a few moments so it stops fuming before you start.

I place the boards to etch into the tank and swirl gently. It takes about 5 minutes to etch a board. As the solution becomes depleted through repeated use, this time gets longer. I use the same solution quite a few times as I tend to make small boards. Dispose of the depleted etching solution properly according to the hazardous material laws in your locale.

When the etching is done, I remove the board with a pair of plastic tweezers and rinse well under running water. The remaining etchant goes into a marked plastic bottle for later reuse.

Ammonium Sulphate

This is apparently a more gentle etchant but is also a bit more fiddly then ferric chloride. I have only used it once many years ago and don't remember many details. It is, however, favoured by many people so if ferric chloride sounds too nasty, Google this one for further instructions.

Hydrochloric Acid / Hydrogen Peroxide

I consider this is the poor man's etchant. It can be made cheaply by combining hydrochloric acid from the hardware store (sold as muriatic acid for cleaning masonry), and hydrogen peroxide from the drug store (used to bleach hair and disinfect wounds). You have to heat this and when you start to etch it gives off some nasty choking fumes. This one is definitely an outdoor or fume hood etchant.

I have used this etchant once and was not terribly impressed. Nonetheless, if other options are not available it does work. Check Google for more details.

Warning: Use Hydrochloric Acid / Hydrogen Peroxide etching solution out of doors.

Removing the Residual Toner

The easiest way to remove the toner once the etching is done is to use acetone or nail polish remover. Do this in an area with good ventilation if you use acetone.

Drilling the Board

Once the board is etched and cleaned, you'll need to drill the holes for the components. In the past I have used 1 mm carbide drills with a 3mm (0.125") shank. These are just a bit large and a 0.8 mm bit would be better.

Carbide Drill Bits

These fit into my handy Dremel Tool. Many people advise using a drill press. I do this freehand and have reasonably good success BUT occasionally I do break a drill bit. I save these broken bits for use in my homebrew CNC machine. Anyway, good thing I bought 10. The bits I bought are made out of carbide as some board materials are very abrasive and apparently can dull high speed steel bits very rapidly. I haven't tried any high speed steel bits so can't offer too much more than that.

Warning: The Dremel drill press I purchased was very poor. The play in the press is virtually guaranteed to snap drills on first use. Perhaps I got a dud.

Next Section: Assembly & Testing